Revolutions measuring instrument

ABSTRACT

An instrument for measuring the revolutions of a rotary body comprising a speed pulse generator for generating a first train of pulses including, in a unit length of time, pulses of the number proportional to the revolutions of the rotary body, a reference pulse generator for generating a second train of pulses including a certain number of pulses in a unit time, and first and second counters for counting the number of pulses appearing in the first and second pulse trains respectively during a counting cycle starting with a certain pulse in the first pulse train; wherein the counting operations of both the counters are stopped simultaneously with the appearance of the first pulse of the first pulse train immediately following the time at which the second counter has counted a predetermined number of pulses, and the number counted by the first counter is divided by the number counted by the second counter, thereby measuring the revolutions of the rotary body.

Sept. 4, 1973 REVOLUTIONS MEASURING INSTRUMENT inventors: IsaoYoshikawa; Takeshi Ochiai,

both of Toyota, Japan Toyota Jidosha Kogyo Kabushiki Kaisha, Toyota-shi,Japan Filed: Mar. 24, 1972 Appl. No.2 237,620

[73] Assignee:

[30] Foreign Application Priority Data June 15, 1971 Japan 46/42835 US.Cl. 317/5, 303/21 CE, 324/160 Int. Cl. G0lp 3/48 Field of Search 317/5,19; 303/21 C, 303/21 CF, 21 CG; 324/160, 161, 178, 179, 186; 307/225[56] References Cited Computer and Apparatus for Measuring RotationalSpeed IBM Technical Disclosure Bulletin, Vol. 13,

No. 4, Sept. 1970 Primary Examiner-J. D. Miller AssistantExaminer--Harry E. Moose, Jr. Attorney-John W. Malley, G. Lloyd Knightet al.

An instrument for measuring the revolutions of a rotary body comprisinga speed pulse generator for generating a first train of pulsesincluding, in a unit length of time, pulses of the number proportionalto the revolutions of the rotary body, a reference pulse generator forgenerating a second train of pulses including a certain number of pulsesin a unit time, and first and second counters for counting the number ofpulses appearing in the first and second pulse trains respectivelyduring a counting cycle starting with a certain pulse in the first pulsetrain; wherein the counting operations of both the counters are stoppedsimultaneously with the appearance of the first pulse of the first pulsetrain immediately following the time at which the second counter hascounted a predetermined number of pulses, and the number counted by thefirst counter is divided by the number counted by the second counter,thereby measuring the revolutions of the rotary body.

ABSTRACT 5 Claims, 7 Drawing Figures 5 l A f -7 a 4 WW5 ML GATEREM/177016 C/RCU/T CULWTER Fp -fzop -3 12 0 2; -/2 l6 /7 T 0 2 I 20a/v/w/va CONTROL f z/ CIRCUIT DEV/CE GATE 7g 5 0cs/LLA770/v J'LHHJI TIMECIRCUIT 9x coulvrm /0 -24 I 23 CONTROL 11mm 6N5 000mm PAIENIEnm'ma sum 10r 4 F/ 6. 2 PR/Of? ART .lllllllHlL FIG. 3

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REVOLUTIONS MEASURING INSTRUMENT FIELD OF THE INVENTION This inventionrelates to a revolutions measuring instrument capable of performingwithin a short period of time digital measurement, with high constantaccuracy, of a wide range of revolutions from low to high speeds.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are diagrams showing theoperating principle of a prior art revolutions measuring instrument.

FIG. 3 is a diagram for explaining the principle of operation of therevolutions measuring instrument according to the present invention.

FIG. 4 is a block diagram showing an embodiment of the invention.

FIG. 5 is a diagram for comparing the measurement accuracy between theconventional instruments and the instrument according to the invention.

FIG. 6 is a diagram for explaining the response time of the instrumentaccording to the present invention.

FIG. 7 is a diagram showing the relationship between said response timeand revolutions.

DESCRIPTION OF THE PRIOR ART There are two main methods of detecting therevolutions in the form of digital signals in such systems as ananti-skid device, electronic fuel injection device and vehicle speedautomatic control device. One is to convert the wheel revolutions into apulse train by means of a gear and a pickup and count the number ofpulses appearing during a certain time T as shown in FIG. 1. The otherconsists in measuring the period t of the pulse signals and obtain thefrequency f by a dividing circuit. Due to the errors which usuallyaccompany the digital measurement, the measurement accuracy drops as therevolutions becomes less in the first method, while the accuracy becomeslower as the wheel speed becomes higher in the second method.

SUMMARY OF THE INVENTION Accordingly, it is an object of the presentinvention to overcome the disadvantages of the conventional instrumentsand to provide a revolutions measuring instrument which is capable ofmaintaining an almost constant measurement accuracy and which requiresonly a short time in measuring low rotational speed.

Another object of the present invention is to provide a revolutionsmeasuring instrument suitable for the driving control of an automobile.

The revolutions measuring instrument according to the present inventioncomprises a speed pulse generator for generating a first train of pulsesincluding, in a unit length of time, pulses of the number proportionalto the revolutions of a rotary body of which the revolutions areintended to be measured, a first counter for counting the number ofpulses in the first pulse train and storing the result, a referencepulse generator for generating a second pulse train containing a certainnumber of pulses in a unit length of time and a second counter forcounting the number of pulses in said second pulse train; wherein thefirst and second counters count the number of pulses appearing in thefirst and second pulse trains respectively during a counting cyclestarting with a certain pulse in the first pulse train, the

counting operations of both the counters are stopped simultaneously withthe appearance of the first pulse of the first pulse train immediatelyfollowing the time point at which the second counter has counted apredetermined number of pulses, and the number counted by the firstcounter is divided by the number counted by the second counter, therebymeasuring the revolutions of the rotary body.

Therefore, it is possible, according to the present invention, to obtainhighly accurate measurement results with only a short time delay. Thisfact makes the instrument of the invention quite suitable for use withan anti-skid device, electronic fuel injection device and vehicle speedautomatic control device, as well as the frequency measuring instrument.Further, this invention is applicable with high accuracy to a frequencymeasuring instrument for general use.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The operating principle of thepresent invention will be explained with reference to FIG. 3. The symbolT shows a predetermined time which has elapsed after the starting ofcounting operation and the symbol T the time which has elapsed after thestarting of the counting operation until the time point where the (n1)th pulse appears, which is the first pulse after the elapsing of T Thetime T and the number of n pulses appearing within the time period of Tare counted by two binary counters. Then the results are applied to adividing circuit in the next stage, where n is divided by T to obtainthe wheel revolutions.

A block diagram for embodying the above-described principle is shown inFIG. 4.

In this drawing, wheel revolutions are converted into an AC signal 4with the frequency proportional to the revolutions by means of anelectromagnetic pick-up 3 and a gear 2 mounted on the wheel 1. The ACsignal 4 is shaped into a rectangular pulse train 6 by a shaping circuit5 and applied to the input terminal of the gate 7 and the clock inputterminal of the flip-flop 12. The flip-flop 12 produces a signal by wayof the portion 6 in response to the first signal of the pulse train 6which appears after the disapperance of the signal 21 applied from thegate 11, thereby opening the gates 7 and 9 to start a counting cycle.The revolutions counter 8 is for counting the n pulses of the train. 6,while at the same time the counter 10 counts the reference pulses 22applied thereto from the oscillation circuit 13 through the gate 9. Whenthe counter 10 has completed the counting of pulses appearing during thetime T the signal 18 is applied to the gate 11, wherefrom the signal 21is applied to the input terminal of the flip-flop 12. The feedback line19 is provided for the purpose of closing the gate 7 by predicting theoverflow of the counter 8 when it reaches the maximum number countablewithin the time T while the feedback line 20 closes the gates l l and 9when the counter 10 has continued the counting operation for the time 2TThe flip-flop 12 may consist of a J-K master slave flip-flop of such aconstuction that an input signal applied to the next stage is delayed bythe time period corresponding to one pulse, so that the input signalappears at the output portions Q and 6 a certain time later. Thisdelayed pulse is synchronized with the revolutions pulse applied to theclock input terminal to produce at the output terminal Q a signal ofhigh potential of the same polarity as the input signal 2i. 'lhis pulseopens the gate M to allow the reference pulse 22 to enter the controlcounter I5. On the other hand, another signal of opposite polarity andlow potential appears at the output terminal Q, whereby the gates 7 and9 are closed and the counters 8 and 10 stop the counting operationthereby to complete a counting cycle.

Thus the revolutions counter 8 stores the number of pulses appearingduring the time period T while the time counter 10 stores the pulsetrain length T which meets the predetermined requirements. The signalsstored in both of these counters are read in the dividing circuit 16 inaccordance with control pulse train 23 produced by the control counter15, and the dividing circuit 16 produces a pulse signal, which may be anumber of pulses corresponding to a binary number repre sentative of ndivided by T, and the pulse signal, is as a rotating speed, applied tothe control device 17.

On completion of the dividing operation, the gate 14 is closed by thesignal 24 and the counters 8 and 10 are reset whereby the signals 18 and21 disappear, until the next appearing pulse train 6 opens the gates 7and 9 to start the next counting cycle.

The feature of the revolutions detecting means according to theinvention described above lies in the fact that the frequency of pulsesproportional to the wheel revolutions is obtained by the digitalcalculation of n/T or the reciprocal of T/n which is an averagefrequency of the n pulses, in order to maintain the measurement accuracyand response speed required by the characteristics of the control deviceto which the invention is applied. I

Explanation will be made now of an embodiment of the invention asapplied to the anti-skid device of the automobile.

In many of the conventional methods of digital measurement of wheelrevolutions employed in the antiskid device, pulses converted from thewheel revolutions are counted as shown in FIG. 1. In these methods,

detection of a sudden change in wheel revolutions is delayed, and thecontrol characteristics of the control device are adversely affected bythe failure to count even a single pulse.

According to the present invention, the number n of pulses and time Tare counted separately from each other by different counters, and thecounting results obtained from the two counters are utilized to obtainthe wheel revolutions, thereby making it possible to detect anyrevolutions quickly with high and constant accuracy.

Explanation will be made now of how accurately the wheel revolutions aremeasured with the calculation circuit according to the presentinvention. It is assumed that T is IOms, that the oscillation frequencyof the oscillation circuit 13 is 100 KHz and that a pick-up is usedwhich produces pulses of 1,000 Hz at the vehicle speed of 50 Km/h. Therevolutions counter 8 and the time counter start and stop countingoperation in synchronism with the wheel revolutions pulses, but thereference time pulses 22 counted by the time counter 10 are out of phasewith the wheel revolutions pulses. Therefore, it will be understood thatthe counting error of 1 bit accompanying the digital measurement isproduced by the time counter 10. The time counter 10, which is a binarycounter with 12 digits, is adapted to count the number of reference timepulses occurring during the time 2T when the signal 18 is producedsimultaneously with the revolutions pulses. As a result, when thevehicle is running at the speed of 5 Km/h, 2,000 reference time pulsesare counted. The counting error in this case is l/2000 or 0.05 percent,whereas the counting error is 0.1 percent or less at the vehicle speedof I50 Km/h when the revolutions counter reaches the overflow state. Ascan be seen from above, the error in the measurement of the wheelrevolutions according to the present invention is always 0.1 percent orless. When the vehicle speed exceeds the 150 Km/h, the gate 7 is closedby the feedback line 19 from the revolutions counter 8, so that theinformation stored in the counter 8 is maintained constant at 30, whilethe information stored in the counter 10 approaches but never exceeds1,000 that is the number of the reference time pulses occurring duringthe time T On the other hand, when the vehicle speed becomes lower than2.5 Km/h to close the gate 9 by means of the feed back line 20 of thetime counter 10, the information stored in the counter 8 becomes 1,while the one stored in the time counter 10 is maintained at 2,000. Thusit is possible to control the measurement of the wheel speed by means ofthe feed back lines 19 and 20.

Now, let us compare the measurement accuracy between the deviceaccording to the invention and the prior art devices. Referring to FIG.5, the abscissa represents the wheel revolutions V(Km/h) and therevolutions pulse frequency flI-Iz), and the ordinate the measurementerror in percent due to the counting error of 1 bit. It is assumed herethat the error occurring in the measurement by the instrument of theinvention is A, those occurring in the first conventional method of FIG.1, B, C and D, and the one occurring in the measurement by the secondconventional method as shown in FIG. 2 is E. The operating time for Avaries between 10 ms and 20 ms depending on the vehicle speed. Thegating times of B, C and D are fixed at 20 ms, 50 ms and I00 msrespectively. The operating time for E varies according to the vehiclespeed. It is also assumed that the reference time pulse frequencies forA and E is KHZ. As will be seen from the drawing, the measurement errorin the first conventional method is inversely proportional to thevehicle speed, while the error in the second conventional method changesgreatly in proportion to the vehicle speed. In contrast, according tothe present invention, the measurement error can be maintained almostconstant below 0.1 percent. For example, when the vehicle speed is 100Km/h, the error in the second conventional method is 2.0 percent and theerror in the first conventional method 1.0 percent, whereas the error inthe present invention is only about 0.095 percent.

Explanation will be made now of the delay time according to theinvention under the above-mentioned conditions, i.e., when T is 10 msand the reference time pulse frequency 100 KHZ. The delay time heremeans the period of time T in sec. from the time point when ameasurement result is obtained of the wheel revolutions V(Km/h) to thetime point when the next measurement result is obtained. In other words,the delay time is the sum of the measurement time T, the time Tprequired to divide n by T and the idle time T before the arrival of thefirstwheel revolutions pulse.

When T is greater than T but not higher than 2T T= (l [20 W 1)l/20V(sec.)

where the square bracket shows the Gauss symbol or the maximum integralnumber derived from the calculation of the equation in the bracket. The(l [20VT,,]) at the right side of the equation (1) shows the number N ofwheel revolutions pulses counted by the revolutions counter. Themeasurement time T is obtained by dividing N by the frequency 20V of thewheel revolutions pulses occurring at the speed of V. The symbol T showsthe 128 clock time required for the dividing operation of binary lldigits, that is to say,

Tp 1.28 (ms) There is a relationship between T and wheel speed V(Km/h) Tk/2OV T where k shows a positive integral number satisfying thecondition From above, the delay time in measurement T T+ T T (l [20VTl/20V+k/20V(sec.)

where k is obtained from the equation (4).

FIG. 7 shows the relationship between T,, and Vwhen T is 10 ms and Tp is1.28 ms. The delay time T never exceeds 14 ms when the speed B is notlower than 25 Km/h, evidently showing that the instrument according tothe invention has a sufficiently high responsiveness as a vehicle speeddetector for use with the anti-skid device.

We claim:

1. A system for measuring the revolutions of a rotary body comprising:

a speed pulse generating means for generating a first pulse traincontaining in a unit length of time pulses of the number proportional tothe revolutions of said rotary body,

a reference pulse generating means for generating a second pulse traincontaining a certain number of pulses in a unit length of time,

a first counter for counting and storing the information on the numberof pulses in said first pulse train,

a second counter for counting and storing the information on the numberof pulses in said second pulse train,

a control means for controlling the period of one counting cycle andcausing the first and second counters to count pulses occurring in thefirst and second pulse trains respectively during said cycle, saidcounting cycle starting with the appearance of a certain pulse in thefirst pulse train and ending with the appearance of the first pulse ofthe first pulse train immediately following the time point at which timethe second counter has counted a predetermined number of pulses, and

a dividing means for dividing the number counted by the first counterduring said counting cycle and stored in said first counter by thenumber counted by and stored in the second counter, thereby to calculatethe revolutions of said rotary body.

2. A revolutions measuring system according to claim 1, wherein saidsecond counter produces a signal when the number counted by said secondcounter reaches a predetermined value, and said control means comprisesa first gate connected between said speed pulse generator and said firstcounter for alternating between the opened state where said first pulsetrain is allowed to pass to said first counter and the closed statewhere said first train is prevented from being applied to said firstcounter, a second gate connected between said reference pulse generatorand said second counter for alternating between the opened state wheresaid second pulse train is allowed to pass to said second counter andthe closed state where said second pulse train is prevented from beingapplied to said second counter, and a flip-flop circuit for controllingsaid first and second gates, said flip-flop circuit applying to eachgate a first gate that is the signal of the first pulse train firstappearing in the absence of any signal in said second counter, saidfirst signal opening said each gate, said flip-flop circuit alsoapplying to each gate a second signal that is the signal of the firstpulse train appearing in the presence of a signal in said secondcounter, said second signal closing said each gate.

3. A revolutions measuring system according to claim 2, furthercomprising a third counter for generating a control pulse train insynchronism with the second pulse train received from said referencepulse generating means, and a third gate inserted between said thirdcounter and said reference pulse generating means for alternatingbetween the opened state where said second pulse train is allowed topass to said third counter and the closed state where said second pulsetrain is prevented from being applied to said third counter, saidflip-flop circuit producing a third signal simultaneously with saidsecond signal, said third signal being applied to said third gate toopen the same, said dividing means being adapted to read out theinformation stored in said first and second counters in response to saidcontrol pulse. 1

4. A revolutions measuring system according to claim 2, in which each ofsaid first and second counters comprises a feedback circuit forgenerating a signal which is applied to said first and second gatesrespectively thereby preventing a pulse from being applied to said eachof the counters when said each counter has completed the counting of apredetermined number.

5. A revolutions measuring system according to claim 1, wherein avehicle wheel speed is to be measured for determining the speed of avehicle therefor and in which said rotary body rotates with revolutionsproportional to the vehicle wheel speed, and the rotational speedobtained by said dividing means is used to control a drive of saidvehicle.

* i i i i

1. A system for measuring the revolutions of a rotary body comprising: aspeed pulse generating means for generating a first pulse traincontaining in a unit length of time pulses of the number proportional tothe revolutions of said rotary body, a reference pulse generating meansfor generating a second pulse train containing a certain number ofpulses in a unit length of time, a first counter for counting andstoring the information on the number of pulses in said first pulsetrain, a second counter for counting and storing the information on thenumber of pulses in said second pulse train, a control means forcontrolling the period of one counting cycle and causing the first andsecond counters to count pulses occurring in the first and second pulsetrains respectively during said cycle, said counting cycle starting withthe appearance of a certain pulse in the first pulse train and endingwith the appearance of the first pulse of the first pulse trainimmediately following the time point at which time the second counterhas counted a predetermined number of pulses, and a dividing means fordividing the number counted by the first counter during said countingcycle and stored in said first counter by the number counted by andstored in the second counter, thereby to calculate the revolutions ofsaid rotary body.
 2. A revolutions measuring system according to claim1, wherein said second counter produces a signal when the number countedby said second counter reaches a predetermined value, and said controlmeans comprises a first gate connected between said speed pulsegenerator and said first counter for alternating between the openedstate where said first pulse train is allowed to pass to said firstcounter and the closed state where said first train is prevented frombeing applied to said first counter, a second gate connected betweensaid reference pulse generator and said second counter for alternatingbetween the opened state where said second pulse train is allowed topass to said second counter and the closed state where said second pulsetrain is prevented from being applied to said second counter, and aflip-flop circuit for controlling said first and second gates, saidflip-flop circuit applying to each gate a first gate that is the signalof the first pulse train first appearing in the absence of any signal insaid second counter, said first signal opening said each gate, saidflip-flop circuit also applying to each gate a second signal that is thesignal of the first pulse train appearing in the presence of a signal insaid second counter, said second signal closing said each gate.
 3. Arevolutions measuring system according to claim 2, further comprisiNg athird counter for generating a control pulse train in synchronism withthe second pulse train received from said reference pulse generatingmeans, and a third gate inserted between said third counter and saidreference pulse generating means for alternating between the openedstate where said second pulse train is allowed to pass to said thirdcounter and the closed state where said second pulse train is preventedfrom being applied to said third counter, said flip-flop circuitproducing a third signal simultaneously with said second signal, saidthird signal being applied to said third gate to open the same, saiddividing means being adapted to read out the information stored in saidfirst and second counters in response to said control pulse.
 4. Arevolutions measuring system according to claim 2, in which each of saidfirst and second counters comprises a feedback circuit for generating asignal which is applied to said first and second gates respectivelythereby preventing a pulse from being applied to said each of thecounters when said each counter has completed the counting of apredetermined number.
 5. A revolutions measuring system according toclaim 1, wherein a vehicle wheel speed is to be measured for determiningthe speed of a vehicle therefor and in which said rotary body rotateswith revolutions proportional to the vehicle wheel speed, and therotational speed obtained by said dividing means is used to control adrive of said vehicle.